As one technique for repairing a kiln wall of an industrial kiln, there has been known a thermite spraying process of: preparing a thermal spray material comprising, as main components, a refractory raw material powder and a metal powder; spraying the thermal spray material to a target surface (a surface to be repaired), using oxygen or oxygen-containing gas as a carrier gas, and melt-adhering the sprayed thermal spray material to the target surface based on heat generated by combustion of the metal powder.
The thermal spraying material for use in the thermite spraying process comprises a metal powder, as just mentioned, so that there inevitably arises a problem that firing is more likely to occur. Therefore, the following Patent Document 1 proposes a firing prevention technique from a viewpoint of a configuration of a thermal spraying apparatus. However, as long as the thermal spray material itself has a firing property, the firing prevention measure only from the viewpoint of a configuration of a thermal spraying apparatus is not sufficient, and a technique for suppressing the firing property of the thermal spray material itself is desired.
As means to suppress the firing property of the thermal spray material, there has been known a technique of using, as a main component thereof, a metal Si powder having a relatively low firing property as compared to other metal powders such as an Al—Mg alloy powder and a Ca—Si alloy powder (as disclosed, for example, in the following Patent Documents 2 and 3).
In addition to the prevention of firing, the thermal spray material is required to suppress dust generation due to the metal powder so as to improve working efficiency and improve bondability (melt-adhering property) so as to perform stable thermal spraying operation with respect to a target surface. As for suppressing dust generation due to the metal powder, the inventors of this application checked the thermal spray material disclosed in the Patent Document 3, in which a metal Si powder contains a fraction having a particle size of 2 μm or less in an amount of 10 mass % or more with respect to the entire metal Si powder. As a result, the inventors found that dust generation due to the metal Si powder notably occurs during thermal spraying operation, causing deterioration in worker's visibility, resulting in significant difficult to continue the thermal spray operation.